To evaluate freehand SPECT (FH) accuracy in the detection and localization of sentinel lymph-node (LN) in patients with breast cancer. Methods: 50 consecutive patients affected by invasive breast cancer cT1-cT2, already scheduled for surgery, underwent lymphatic mapping (standard procedure with intradermal administration of 60-80 MBq of Tc-99m nanocoll). Subsequently patients were scanned using a FH system (prototype of CSS300 by SurgicEye?). The position and orientation of a gamma probe is acquired simultaneously with its read-out using an optical positioning system. After obtaining synchronized readings from a free hand scan containing the ROI, the information is used to reconstruct 3D images using ad hoc models. FH results (number and localization of the sentinel LN) were compared for reference with standard Planar Scintigraphy (PS) (lateral and diagonal views). Results: In all patients PS mapped at least one LN in the axilla, while FH managed to identify at least one LN in 49 out of 50 patients resulting in 98% sensitivity. Overall PS detected 91 LN, while FH identified 76/91 LN: on a LN basis, both sensitivity and accuracy resulted in 84%. In 10 patients FH detected fewer LN than PS: 15/91 false negative sentinel LN at FH. In 1 patient FH was able to detect 1 LN more than PS. False negative results (15 LN) were probably due to low tracer migration to sentinel LN, insufficient FH scanning time or too close LN that ended up merging. FH showed 1 additional spot in 6 patients and 2 additional spots in 2 patients easily recognized as artefacts with no risk of misunderstanding. Conclusions: These preliminary data show that FH technology is able to localize sentinel LN in the axilla adding 3D information that could be potentially useful in the operating room. This could help surgeons for an easier image guided sentinel LN dissection.

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